This invention relates to electrical stepping motors and particularly to stepping motor structural arrangements and manufacturing methods which afford motors capable of a wide variety of stepping angles.
Stepping motors are capable of rotating in steps over precise angles in response to particular applied current.
U.S. Pat. No. 3,842,332 discloses such a stepping motor. Here five phase windings W.sub.1 -W.sub.5 are disposed on 5u stator poles, such as 5 .times. 2 stator poles I, II, III, . . . X (with u = 2). The factor u is an integer. It indicates the number of stator poles having the same polarity among the phases.
To maintain the accuracy available from stepping motors, it is undesirable for a stepping motor to apply its rotation through intermediate angle multipliers such as gears which might reduce the step prevision. For stepping motors to apply rotation directly to a load each stepping motor must move through the same stepping angle required by the load.
In order to satisfy the wide variety of stepping angle requirements of stepping motor users, a stepping motor manufacturer must carry a large inventory of electrical sheet-steel stator laminations. Normally each different lamination type is used for one size of stepping angle. However, the different dies for cutting each type of lamina are expensive. Also, the number of stepping motors manufactured for many applications is often small. Thus the extensive inventory is quite uneconomical.
Attempts have been made to reduce the extent of the variety of stator laminae required in inventory and still allow assembly of motors with a wide range of stepping angles and speeds. One such attempt is disclosed in the aforesaid copending U.S. patent application Ser. No. 500,001. This involved changing the stepping angle .phi. of the motor in the aforementioned U.S. Pat. No. 3,842,332 into five different stepping angles .phi./4, .phi./2, .phi., 1.25.phi., and 2.5.phi. within one and the same motor, by changing the winding connection and drive connections. The motor connection for the largest stepping angle could be operated as a two-phase synchronous motor. With a stator of given electrical sheet-steel lamina and a given rotor, it is possible to obtain five different stepping angles from the same motor structure.
However five stepping angles are only a small fraction of the desired stepping angles.
The aforementioned application also discloses that the motor operates even when, within a limited region, the stator tooth pitch T.sub.s varies relative to the rotor tooth pitch T.sub.R. Specifically it shows that T.sub.s may vary between 0.9T.sub.R and 1.1 [(n + k + 0.6)/(n + k)]T.sub.R, where n is the whole number of stator tooth spaces per stator pole, and k is the whole number of stator tooth pitches that fit between poles.
An object of this invention is to improve stepping motors.
Another object of this invention is to improve stepping motor manufacturing systems and methods.
Another object of the invention is to make it possible to obtain a large number of possible stepping angles from a limited number of and possibly one stator laminae shape.